Method and apparatus for separating fragmentary minerals of different specific gravities in crushed ores



Dec. 13, 1938. 3 E4 WUENSCH 2,139,789

METHOD AND APPARATUS FOR SEPARATING FRAGMENTARY MINERALS OF DIFFERENTSPECIFIC GRAVITIES IN.CRUSHED oREs Filed Feb. 4, 1953 2 Sheets-Sheet 1 H/N VE/VTOR.

g MW.

ATTORNEY.

Dec, 13, 1938. r Q E, WUENSCH 2,139,789

METHOD AND APPARATUS FOR SEPARATING FRAGMENTARY MINERALS OFDIFFERENT'SPEGIFIC GRAVITIBS IN QRUSHED ORES Filed Feb. 4, 1.953 2Sheets-Sheet 2 //V l/EN 701?.

A TTORNEX Fatented Dec. 13, 1938 PATENT OFFICE METHOD AND APPARATUS FORSEPARAT- ING FRAGMENTARY MINERALS OF DIF- FERENT CRUSHED ORES SPECIFICGBAVITIES Charles Erb Wuensch, Berkeley, Calif., assignor to WuenschHetero Concentration Process Company, Wilmington, Del., a corporation ofDelaware Application February 4, 1933, Serial No. 655,196

9 Claims.

This invention relates to a method and apparatus for separatingfragmentary minerals of different specific gravity in crushed ores, and

more particularly to a novel method and apparatus for employing a heavyfluid, such as finely comminuted heavy minerals or solids suspended inwater so as to form what may be termed a heavy fluid medium forgravitationally classifying or separating the several constituents ofdifferent specific gravities contained in ore or rock.

The use of chemicals of high specific gravity to effect the separationof mineral constituents of an ore or rock is well understood by thoseskilled in the art. In this practice, the specific gravity of the heavychemical is varied with diluents so as to float one mineral and sink theother. Satisfactory separations can be made where there is as little as0.05 of a point difference in specific gravity, whereas other methods ofconcentration, such as jigging or tabling, require at least one point ormore difference to effect a satisfactory separation. However, the costof such heavy.

density chemicals is so great that the inevitable small losses rendertheir use prohibitive in large scale commercial operations.

Numerous attempts have been made to substitute finely comminuted heavyminerals or solids suspended in water to form a heavy fiuid formedium.of the expensive chemicals. The use of such solids suspended inwater is nothing but a form of classification in which hindered settlingis carried to the point where an endeavor is made to control the densityof the hindered settling column so that the solid water suspension actsthe same as a chemical of high specific gravity.

The difiiculties-inherent in attempting to control the density of thisheavy fluid column so as to get the same effect as with a chemical ofuniform density are familiar to anyone experienced in ore dressing.Uniform maintenance of the required density of the heavy solid fluidsuspension composed of particles of different densities, sizes andshapes, even though finely comminuted, is obviously impossible becauseof the constant variations of conditions when the one feed is added andthe contaminationof the medium itself by the constituents of the ore.

Heretofore, in practically all processes involving modifications inmanipulations to make a solid Water suspension behave like a uniformchemical of heavy density, the ability to concentrate ores in generalhave been suggested. However, these processes have only been successfulin washing coal, where the density of the (Cl. I 209-473) fluid masscolumn need not be controlled to such a degree as would be required foreconomic results I in ore dressing, because of the low specific gravityof the coal itself and because of the relatively wide gravity rangebetween the various particles varying from coal at one end to refuseproper at the other. In addition to this, such operations are just thereverse to that required in ore concentration. In coal washing, the coalfloats as a tailing and the refuse sinks as a concentrate; Therefore,the contamination of the medium in coal washing, where the refuse slimesto a large extent may constitute the separatory medium, presents a muchsimpler problem, than in ore concentration. Therefore, it is one objectof this invention to provide an improved method and apparatus that shallproperly utilize and coordinate collectively all of the underlying basicprincipals for effecting the delicate separations required in theapplication of heavy fluids to ore concentration.

In all the processes known tome suggesting methods of manipulation tocreate conditions so as to make the use of a solid water suspensionapproximate the separatory effects of a uniform chemical of highspecific gravity, the processes have sought only the creation of. aperfect solid water suspension to produce the separatory effects ofa--uniform, heavy chemical, and all sight was lost of the fact thatlaboratory sink and float.

tests have always been made as a batch operation and not for large scalecontinuous operations. In the latter, many other factors besidesspecific gravity enter into the problem, such as time, velocity, surfacetension, crowding, purification of medium and size of particles.

All of the processes that have heretofore been proposed fall short ofefiecting as delicate a separation as a heavy chemical. These processesinclude inherent factors that are not absolutely sound, and theapparatus fail to apply properly the basic principles, such as theinfluence of surface tension, resistance amongst various sizedparticles, velocity relatlonship, and soforth.

It is-well known that, in the finer sizes of ore particles, such asslimes, no gravity separation is possible, because of the large surfaceareas, as compared to volume and weight, whereby the surface tensionforces are greater than the forces due to differences in specificgravity. In the heavy mediums, the surface tension and viscosity factorsexert marked effects on even relatively coarse sand particles up to A"in size. The result is that, when material is fed to those apparatusemploying a; cone, the smaller sizes of materials of the same specificgravity rise to the top of the cone more easily than the largerparticles. The larger tailings particles must, therefore, break throughthe upper bed of fine tailings in order to be discharged over the top ofthe cone. This results in excessive crowding and the loss of some lightmiddlings.

These factors also prevent the finer particles of concentrates fromsinking to the bottom of the cone, because of the impossibility of 100%screening efliciency on the material that is fed to the cone to removethe finer sizes of particles, and also because of a small amount ofattrition during treatment, these fine heavier sand particles cannot bekept out of the medium. This, therefore, creates an excessive denseandviscose zone at the bottom of the cone and makes it impossible tomaintain a perfectly graduated differential density column where thereis not over 0.1 or 0.2 of a point difference in specific gravity betweenthe top and bottom of the cone. This combination also adds to theexcessive crowding pointed out above, with a resultant loss of valuablemiddlings with the tailings. These processes recognize only densityconditions and fail entirely to provide factors to ofiset the crowdingeffects, and, consequently, perfect separation is not obtained. Thefundamental laws of viscous and turbulent resistances are ignored. Thevertical component of this crowding force is less than the horizontalcomponent, and, therefore, the lighter middlings move laterally morereadily than downwardly, and as they spread out and reach the peripheryof the cone, where the velocity, due to the rotation of the cone or anagitator therein, is greatest, these lighter middlings have a tendencyto discharge with the tailings rather than to be crowded down and sinkwith the concentrates. I

Therefore, another object of this invention is to provide a novel methodand apparatus for classifying or separating the mineral constituents ofan ore in accordance with the specific gravity of such constituents,wherein the apparatus is adapted for continuous operation and provides aseparatory effect that will be the resultant of density, time, velocity,crowding, surface tension and size of particles.

i The above and other objects will be made apparent throughout thefurther description of the invention, when taken in connection with theaccompanying drawings. It is to be distinctly understood that thedrawings are not a definition of the invention, but merely a:diagrammatic fiow sheets illustrating one manner in which the processmay be carried out, the definition of the in-' vention being defined bythe appended claims.

In the drawings:-

Fig. 1 is a diagrammatic flow sheet of an apparatus embodying theinvention.

Fig. 2 is an enlarged detail view of a part of the apparatus illustratedin Fig. 1.

Fig. 3 is an enlarged detail view of the separatory trough embodying theinvention, and

Fig. 4 is a sectional view taken on line IVIV of Fig. 2.

For the sake of simplicity, the apparatus will be described inaccordance with the operation in carrying out the various steps of theprocess.

Referring to the drawings, the crushed ore is fed upon a vibratingscreen, represented in its entirety by H), where it is thoroughly washedby numerous water sprays II for removing the smaller particles of thematerial, such as the -20 mesh material, which material is preferablytransferred direct to a classifier l2, in a closed circuit l3, with aball mill I I. This product is then ground to about 60 mesh and theoverflow goes directly to an ore pulp thickener I5, from which point thethickened ore pulp is sent to a flotation, cyanide or other finishingplant for producing a marketable concentrate. The purpose of thisthorough washing of the crushed ore is first to eliminate the -20 meshmaterial, which on account of the viscosity of the heavy fluid and itssurface tension effects on the finer sizes, renders this fine productunsatisfactory for separation by the present process. Also it isexpedient to thoroughly wet the -1" to 1 plus 20 mesh material beforedelivering it to the separatory trough Hi. This film of water on theparticles greatly facilitates the removal of the medium from the oreparticles in the subsequent washing steps and also assists in dilutingthe top of the medium in the separatory trough so as to slightly reducethe specific gravity of the top zone in the flowing medium column in thetrough.

As the ore feed enters the trough l6, by way of a suitable passageway orchute H, from the screen ID, the medium from the medium mixing trough 20is introduced with it by way of a conduit l8. In the medium mixingtrough, the density of the medium is automatically controlled byblending the return medium from the separatory trough with varyingproportions of the thickened medium. This maintains the mediumabsolutely at a constant point. A float control I9 is provided in themedium mixing trough 20 for controlling the volume of the return mediumentering the separatory trough Hi.

In the separatory trough there is considerable violence at the entrancepoint, indicated, generally at A, and due to the splash practically allof the feed is submerged to substantially the lower middle zone of thetrough. On the rebound, the finer and lighter gangue particles risefaster than the middlings and heavier concentrate particles,respectively, because the finer and lighter particles do not penetratethe medium as deeply as the larger and heavier particles. This resultsin trapping the lighter middlings below the supernatant bed of tailings.,The bottom of the separatory trough I6 is slightly inclined downwardlyfrom the receiving end toward the tailing-discharge end, as shown.Within the separatory trough and extending horizontally thereof andpositioned adjacent the bottom thereof, and underlying the feed conduitI1, is provided a conveyer, represented in its entirety by 2 I. Thisconveyer is preferably a spiral conveyer andoperates as an agitator inthe lower zone of the trough, and also serves to move the heavierconcentrates and middlings upwardly of the trough incline and to theright of the trough, as viewed in the drawings, to the concentrate trap,represented in its entirety by 22.

Within the trap 22 is provided a jigging compartment 26, for the purposeof producing two (a concentrate and heavy middlings) products. This isan important feature of the invention and can be employed in extendingthe utility of the apparatus and process as a cleaner instead of usingit only as a, roughing device to eliminate the lighter gangue orlow-value materials. The jigging compartment 26 operates to assemble theheavier larger concentrates to form a bed superimposed on the screen 23within the trap 22, and as the bed of larger concentrates builds up, theheavier middlings within the trap 22 will be forced upwardly and intocontact relation with the conveyer 2| and carried to a middling trap 21.Thecoarse concentrates, as they build up, are dischrged through thewell, indicated by the arrow shown in Fig. 4, to join the finer productpassing throughthe screen '23, where they are removed by a suitableelevating device 24 to washing screen 25. The middlings which build upin jigging compartment 26 and are conveyed by conveyor 2| -maybe removedby a scraper wheel 28 or any suitable type of elevator and transferredby way of a passageway 29 to the washing screen 25, or to a separatewashing screen (not shown),

' these lighter middlings gradually work their way longitudinally of thetrough (from right to left in the drawings) toward the tailing exit ordischarge to a point above a light middling trap 3|. 3

At this point, a very small amount of water may be introduced into thetrap 3|, as indicated at 32, in order to reduce the density of themedium at this point and thereby facilitates sinking and trapping eventhe lightest middling particles and finest sand particles. Theelimination of these fine sand particles assist greatly in purifying themedium.

These middlings within the moved by a suitable lift or pump, by way of apassageway 33, onto a screen, represented in its entirety by 34, wherethe medium is drained off of the middlings and returned to the trough byway of a conduit 35, preferably intermediate the middling trap 3| andthe adjacent overflow outlet,..andthus rethicken the medium after it hasbeen diluted with water in the zone overlying middling trap 3|. Themiddlings and fine sandy impurities collected by the screen 34 aretransferred to the washing screen 25, or to a, separate washingscreen(not shown), by. way of a passageway 36, where the medium is removed andrecovered in a medium thickener 31.1

The natant tailings overflowing at the lower end (left end in thedrawings) of the separating trough l6 are conveyed by way of a' chute orpassageway 38 to a vibrating screen 39 which partially removes themedium adhering to the tailings. The medium that filters through thescreen 39, without any washing since it is the low gravity surfacemedium from trough I6, is returned to the medium mixing trough 2|! byway of a conduit 4|, with the assistance of a suitable pump 42. Thetailings then pass onto another screen 43, where the remaining mediumadhering thereto is removed and eventually recovered in the 1 samemedium thickener 31 as that removed from the concentrates and middlings.The tailings go to waste and are sent to a point of distribution bymeans of a conveyer or the like.

The wash water from the several washing screens pass over a vibratingscreen 44, the latter being of substantia ly 150 mesh, before go ng tothe medium thickener. The 150 mesh vibrating screen operates toeliminate the l or 2% of plus 20 mesh material and fine sandy material,

which was not removed from the feed because of slight inefficiency. inthe initial screening plant I. These impurities are transferred througha trap 3| are re-- suitable passageway from the 150 mesh vibratingscreen to a concentrate bin 48 containing the concentrates and middlingproducts, where they are subsequently conveyed to their original 20 meshmaterial in the ball mill classifier circuit, above mentioned.

Additional medium is prepared in a small auxiliary ball mill classifiercircuit, represented in its entirety by 41. The medium from this ballmill classifier circuit is supplied to the medium thickener 31 forbuilding up the diluted medium from the several washing screens tocompensate for the small losses of medium during the process. This maybe done periodically.

Above the medium thickener 31 there is provided two reagent feeders 48and 49. One of these feeders 48 may be employed for adding a reagent,such as lime, or, in some instances, acids may be required to controlthe p. H. in the thickener. This reagent must be'varied for eachparticular ore in order to get the optimum settling conditions. Theother reagent feeder 49 may be employed for adding a reagent, such assodium silicate, alum, or some other suitable dispersion or fiocculatingreagent to effect a selective dispersion of the small amount of gangueslimes that may remain in the diluted medium, as well as to flocculatethe medium slimes. The overflow of the medium thickener 31 containingthe gangue slimes with a very small quantity of the medium slimes aretransferred to the ore pulp thickener, by way of a passageway 5|, wherethe valuable constituents are recovered in the subsequent finishingsteps. It is here pointed out that experiments have shown that theover-all medium loss isf less than one pound of medium solids per ton oore. 1

Novel means are provided for automatically regulating the amount of feedto the separatory trough l6, which means may comprise a suitablecontrol, such as a Pitot tube 52 or viscometer, adapted to actuate arheostat 53, the latter being ooeratably connected to a motor driven orefeeder 54, the ore feeder 54 being positioned to receive ore from asupply source 55 and transfer the same to a secondary crusher 56, wherethe ore is conditioned for delivery to the original vibrating screen ID;the Pitot tube 52 being responsive to 'ings uniform.

After the diluted medium has been reconditioned in the medium thickener31, it is transferred by way of a passageway 51, with the assistance ofa suitable pump 58, to a surge tank 59. The surge tank 59 is preferablyprovided with a suitable agitator 6| for maintaining the propersuspension of the solids in the medium. As above stated, the mediumseparated from the tailings, by the screen 39, is returned by way ofElse passageway 4| to the medium mixing trough Since it is necessary tomaintain a constant medium level, as shown at 62,. in the medium trough20, a suitable by-pa s 63 within the passageway 4| is provided forby-passing the medium, by way of a passageway 64, into the dilutedmedium passageway 66, leading to the I mesh screen 44, where it isthereafter transferred to the medium thickener 31. medium is preferablycontrolled by blending in the mixing trough 20 the light density returnThe density of the medium from the passageway 4| with the thickenedheavy medium from the surge tank 59.

A sensitive inverted submerged pressure tube or density gauge or ahydrometer ii is provided within the medium mixing trough, and below themedium level, the gauge 1| being operatively connected to a rheostatcontrol 12 for automatically operating a valve 13 for supplying theproper amount of thickened medium to the medium mixing trough by way ofa passageway 14 for maintaining the' density within the medium trough 20at a predetermined point. A high speed agitator 15 is preferablyprovided adjacent the bottom of the mixing trough 20, and extendinglongitudinally thereof, for maintaining the proper suspension andblending of the solids in the medium.

The fioat 9 operates to control the medium level in the trough 20, andisoperatively connected to a icy-pass 63 for varying the amount of thereturn medium to the medium mixing trough and by-passing the' remainderto the medium thickener circuit 66. This float I9 also controls thevolume of medium that is supplied to the separatory trough l5, as abovementioned.

The medium within the separatory trough I6 inherently possesses a slightdensity differential. In general, the top gravity should be 0.1 to 0.2of a point lighter than the bottom gravity and 0.05 lighter than thelightest tailing particle. This permits the wetted feed to sink belowthe surface of the medium as it falls into the trough It. Thiscompensates for the turbulence set up by the incoming feed, and also forthe surface tension effect on the finer sizes of gangue. Initially, thefeed, regardless of the specific gravity of the particles, tends to sinktothe middle zone of the separatory trough. However, on the rebound, thefiner sizes of the gangue particles, due to surface tension are liftedahead of the coarser gangue particles. The middlings rise slower and areconsequently trapped below the tailing bed instead of having to breakthrough from above the tailing bed, as in. the prior process.

Particular attention is directed to the novel construction and operationof the conveyor 2| within the separatory trough. The axis of theconveyor 2| is inclined substantially the same amount as the bottom ofthe separatory trough l6, and that portion of the conveyer 2| to theright of the light medium trap 3| is of considerable larger diameterthan that portion of the conveyer at the left of the middling trap 3|and the conveyer blade is preferably omitted overlying trap 3| Thepurpose of the larger portion at the right of the middling trap 3|, asviewed in the drawings, is to provide an undertow for drawing themiddlings suspended just above the conveyer downwardly and intoconveying relation with the conveyer, to convey the concentrates andmiddlings to their respective traps, and to induce a counter-currentbelow the surface of the medium, which current operates to carry thesuspended lighter middlings down the trough to a point above themiddling trap 3|, at which point the current within the trough forms azone of unagitated quiescence, permitting the lighter middlings to sinkin the trap 3|, facilitated, if desired, by the minute dilution of themedium at this point by the means 32. This point of quiescence is alsopartially due to the particular shape of the mixing trough is, whichtrough gradually increase in cross sectional area from the upper orright end to the lower or left the separatory the control of veyerblades at the left of the trap 3| preferably taper in crest to crestdiameter from the trap 3| toward the discharge end. This'diametraldecrease in the conveyer permits a decrease in the inclination of thebottom of the trough adjacent this portion of the conveyer, whichassists in checking the current and forming the zone of quiescence abovethe trap 3|. Also it will be noted that the heavy bottom medium returnedfrom the bottom of trap 3| to the light middling screen 34, by way ofpassageway 35, is delivered within the trough l6 at a point adjacent'the discharge end, the density of which medium will assist in thedischarge of the tailings over the discharge end of the separatorytrough, as well as decrease the differential of density in the mediumcolumn from the top to the bottom of trough at the discharge end.

It is here pointed out that in actual practice, gravity of the medium isobtained by grinding the solid particles in the medium not greater. thanapproximately 200 mesh, but when an endeavor is made to grind the solidconstituents of the medium to substantially 200 mesh or finer, thatactually only about 10% will be of this size and the balance vary inproportions from 200 mesh down to 500 mesh, or even finer. Therefore,when the medium flows toward the tailing discharge end of the separatorytrough, there will be a stratification and classification with the finerslime particles, and hence a lighter density medium near the surface. Itis also pointed out that the velocity factor of the present processinvolves many details and components. The mean velocity is controlled bythe slope of the trough, and the induced cross-currents set up by theconveyer. The velocity-is least nearest the sides and bottom of thetrough and greatest at a point slightly below the surface of the medium.When the feed is dropped into the separatory trough, stratificationtakes place, due to specific gravity of the particles, and, to a limitedextent, due to the size and shape of the particles. The velocity of flowbeing almost uniform, has little effect on various sizes and shapes ofthe gangue particles, but it greatly accentuates even minute differencebetween the particles of difierent specific gravity, by virtue of theirsuspension in the medium.

The rotation of the spiral conveyer in the separatory trough counter tothe flow of the medium creates an undertow and induces a current in thedirection of the normal stream flow just below the zone of maximum flow.The concentrates and heavier middlings are conveyed upstream while thefiner gangue particles rise nearest the surface in the top part of thezone of maximum flow, and the larger gangue particles rise to a pointjust below the zone of maximum velocity. The intermediate sizes ofgangue collect along the upper sides of the trough. The lightermiddlings which are too light-to be conveyed upstream with theconcentrates, arrange themselves amazes below the tailings. Therefore,inasmuch as the crowding effect has a greater component laterally thanupwardly or downwardly, as above pointed out, any crowding causeslateral readjustment in the upper tailing zone, so as to mix anddistribute more or less uniform particles of different sizes of the samegravity. This tends to make the flow velocity more or less uniformthroughout the channel and provides an ideal condition for preventingthe formation of zones of excessive velocities which are inherent inother types of apparatus.

The-lighter middlings are removed continuously by way of the trap 3| andnever reach the tailing end or discharge point. As the tailings reachthe discharge point, they flow more rapidly than at any point in thetrough, due to the velocity of approach. This also provides a lateralflow differential with the smallest velocity at the point of feeding, asubstantially uniform flow to middlings trap 3| and progressivelyincreasing towards the discharge end. Because of the fact that all alongthe trough the volume of material is reduced by the continuous removalof concentrates and middlings, no harm results when the velocityincreases at the discharge point, since the valuable constituents of theon have already'been removed.

Other important features of the present process and apparatus includesthe complete clarifying of the effect of the different sizes ofparticles, greatly minimizing the crowding effect, compensation for thesurface tension effects on the finer sizes of particles, the automaticfeed for supplying the ore to the separatory trough, the novel jiggingcompartment on the concentrate end so as to make two or moreconcentrated prodnets, and, thereby extending the utility of the processand apparatus as a cleaner instead of using it only as a roughing deviceto eliminate the lighter gangue material. The continuous removing of theheavy fine sand particles of concentrates will accumulate in the medium,thereby preventing excessive specific gravity of the medium at thebottom of the separatory trough; the introduction of water in the lightmedium trap and the returning of this heavy bottom medium near thetailing end of the separatory trough, and causing a dimunition of thedifferential in the differential density column near the tailingdischarge; the processive removal of concentrates and middlings;together with the harmonius functioning of these various factors forbringing about a condition vital for savin the lightest middlingparticles.

While I have illustrated and described one form of an apparatus forcarrying out the present method, it will be apparent to those skilled inthe art that various changes, modifications, substitutions, additionsand omissions may be made in the method and apparatus without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

I claim:

1. The method of separating fragmentary materials of differing specificgravities, which includes the steps of feeding a supply of such materialinto a fluid medium composed of liquid and comminuted particles ofsolid' matter, inducing a flow of medium and fed material in oppositedirections at different levels toward separate outlets, agitating themedium in the lowest zone while maintaining a zone thereabove morequiescent, and providing within the lowest zone a zone intermediate saidoutlets more quiescent than in the other portions of the lower zone.

2. The method of separating fragmentary materials of diflering specificgravities which includes the steps of feeding a supply of such materialinto a fluid medium composed of a liquid and comminuted particles ofsolid matter, inducing a flow of medium and fed material in oppositedirections at different levels toward separate outlets, agitating themedium in the lowest zone while maintaining a zone thereabove morequiescent, providing within the lowest zone a zone intermediate saidoutlets more quiescent than in the other portions of the lower zone, andincreasing the velocity of flow of the medium in the upper quiescentzone adjacent the lower more quiescent zone.

3'. The method of separating fragmentary maproviding withinthe lowestzone a zone intermediate said outlets more quiescent than in the otherportions of the lower zone, and separately removing particles of the fedmaterial from the respective zones of the different levels andseparately removing other particles of the fed material from the morequiescent zone within the lower zone.

4. The method of separating fragmentary materials of differing specificgravities which includes the steps of feeding a supply of such materialinto a fluid medium composed of a liquid and comminuted particles ofsolid material, agitating the medium in the lower zone thereof whilemaintaining a zone'thereabove more quiescent, inducing a counter-currentfiow in the respective upper and lower zones, and providing a zoneintermediate the length of flow wherein the medium is maintained morequiescent from top to bottom than in the lower agitatedvzone.

5. The method of separating fragmentary materials of differing specificgravities which includes the steps of-feeding a supply of such materialinto a fluid medium composed of a liquid and comminuted particles ofsolid matter, agitating the medium in the lower zone thereof whilemaintaining a zone thereabove more quiescent,

inducing counter-current flow in the respective upper and lower zones,providing a zone intermediate the length of flow wherein the medium ismaintained more quiescent from top to bottom than in the lower agitatedzone, and separately removing particles of the fed material from therespective zones of the different levels, and separately removing otherparticles of the fed material from the zone wherein the medium agitatedportions of the lower zone, and separately removing ore and medium fromdifl'erent levels and separately removing another portion of ore andmedium from the more quiescent portion 01 the lower zone, and feedingadditional medium to the fiowing mixture of ore and medium at a pointintermediate the more quiescent portion of the lower zone and the outletof the less agitated upper zone.

7. An apparatus for separating fragmentary materials of differentspecific gravities including an elongated trough, said trough having anoutlet at an upper portion and being adapted to contain a compound massof fragmentary material to be separated and a heavy fluid mediumconsisting of finely comminuted matter and a liquid, conveyor means inthe lower portion of said trough adapted for conveying portions 01' thecompound mass in the lowest zone of the trough and simultaneouslyagitating the compound mass in the trough, means to feed a supply offragmentary material to said trough above the zone of the conveyor andagitator means, said conveyor having intermediate the feed means and thesaid upper outlet of the trough, a portion in which the agitative andconveying capacity of the conveyor is reduced thereby providing a zoneof quiescence intermediate said feed and said upper outlet, a trapunderlying the zone of quiescence, a trap for receiving material fromthe conveyor, and a circuit for receiving medium from respective outletsof the trough, said circuit including a thickener, a purification screenfor medium and wash water ahead of the thickener, and a mixing troughfor receiving diluted medium and thickened medium, said mixing troughincluding means operatively responsive to the viscosity oithe medium inthe mixing trough for regulating the inflow to said trough of thickenedmedium and diluent.

8. A method of separating heterogeneous mixtures of solid particleshaving different densities which comprises washing and draining themixture, introducing the mixture while still moist into a body of heavyfluid medium, withdrawing relatively heavy solid particles contaminatedwith medium from a lower portion of the body, with-- troducing themixture of predetermined density' into the body of medium.

9. A method for separating a mixture 01' light and heavy ore particleswhich comprises introducing the mixture into a body of heavy fluidmedium, withdrawing the light particles contaminated with medium from anupper portion of the body, withdrawing the heavy particles contaminatedwith medium from a lower portion of the body, washing the ore particlesthus withdrawn to cleanse them of medium and dilute the medium, settlingthe diluted medium in a thickening chamber, withdrawing the thickenedmedium from a lower portion of the thickening chamber, withdrawingliquid and ore slimes from an upper portion of the thickening chamberthus removing ore slimes from the circuit, adjusting the density of thethickened medium to a predetermined point and then returning it to thebody.

C. ERB WUENSCH.

